Halogen-free flame resisting synthetic resin composition

ABSTRACT

The present invention relates to a self-fire distinguishable halogen-free flame resisting synthetic resin composition obtained by adding 0.5 to 15 parts by weight of synthetic silicate (also called &#34;hydrated silicic acid&#34; or &#34;wet silica&#34;) to 100 parts by weight of a mixture comprising 70 to 30 parts by weight of at least one thermoplastic synthetic resin and 30 to 70 parts by weight of magnesium hydroxide or aluminum hydroxide having an average particle size of 0.1 to 10 μm. 
     This composition is white semitranslucent unlike the one containing carbon black according to the prior art, so that it is suitable for decorative use including floor materials and wall covering materials.

TECHNICAL FIELD

The present invention is appliable to the field of preparing a syntheticresin composition of a flame resisting material.

BACKGROUND ART

Recently, a wide variety of flame resisting synthetic resin compositionshave been developed with the purpose of ensuring the safety against afire. Among them, flame resisting synthetic resin compositions notcontaining halogen, phosphorus or antimony trioxide, i.e., so-callednon-toxic flame resisting synthetic resin compositions of a halogen-freetype are given special attention.

Generally, such a flame resisting synthetic resin composition of ahalogen-free type contains an inorganic filler such as aluminumhydroxide or magnesium hydroxide. Further, the amount of the inorganicfiller required to obtain sufficiently high flame resisting effect isgenerally 30 to 70% by weight based on the composition. However, asynthetic resin composition containing an inorganic filler in such ahigh content does not generally exhibit well-balanced strength, so thatit is brittle and poor in processability.

Further, some synthetic resin compositions containing such a flameresistant filler alone do not exhibit sufficient flame resistance. Thusthe simultaneous addition of such a filler and carbon black has beenattempted with the purpose of overcoming these problems (see JapanesePatent Publication No. 10898/1982). The simultaneous addition thereof isknown to impart high flame resistance to a synthetic resin, even whenthe amount of a flame resistant filler is relatively small. However, thehalogen-free flame resisting compositions thus prepared are all black,so that they can not be applied to the fields wherein colordiscrimination is necessitated or the fields wherein importance isattached to appearance, i.e., the fields wherein the use of a blackmaterial is unfavorable (for example, wall covering material).

DISCLOSURE OF INVENTION

An object of the present invention is to provide, without using carbonblack, a halogen-free flame resisting synthetic resin composition. Thusmaking it widely appliable to the field wherein a color-discriminableflame reisting composition must be used. In addition to fields whereinimportance is attached to appearance, for example, wall coveringmaterial.

More particularly, the present invention relates to a self-fireextinguishable, halogen-free and flame resisting synthetic resincomposition. This is obtained by adding 0.5 to 15 parts by weight of asynthetic silicate (also called "hydrated silicic acid" or "wet silica")to a mixture comprising 70 to 30 parts by weight of a thermoplasticsynthetic resin and 30 to 70 parts by weight of magnesium hydroxide oraluminum hydroxide having an average particle size of 0.1 to 10 μm.

BEST MODE FOR CARRYING OUT THE INVENTION Synthetic Resin

The synthetic resin to be used in the present invention may be any oneas far as it is thermoplastic, and examples thereof include crystallinepolyolefins such as polyethylene, ethylene-vinyl acetate copolymer(abbreviated to "EVA"), ethylene-ethyl acrylate copolymer (abbreviatedto "EEA"), ethylene-methyl methacrylate copolymer (abbreviated to"EMMA") and polypropylene (abbreviated to "PP"), polystyrene,polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer(abbreviated to "ABS"), nylon-6 and nylon-6,6. It is preferred from theviewpoint of the strength of the resulting composition that the resinhave a melt index of 0.2 to 10.0.

Inorganic flame retardant

The inorganic flame retardant to be used in the present invention isaluminum hydroxide or magnesium hydroxide having a particle size of 0.1to 10 μm.

According to the present invention, such a flame resistant filler may beadded in an amount of 30 to 70% by weight based on the composition tothereby impart flame resistant effect to the resin.

Synthetic Silicate

The synthetic silicate to be used in the present invention is generallycalled "hydrated silicic acid" or "wet silica". Further, it does nothave a specified crystalline structure but a network structure of Si-O,so that it is also called "amorphous silica". The synthetic silicate maybe any one containing 40 to 70% by weight of SiO₂ as a major componentand 10 to 45% by weight of MgO and CaO as secondary components.Particularly, a synthetic silicate containing 50 to 60% by weight ofSiO₂ and 12 to 30% by weight of MgO and CaO and having an ignition lossof 10 to 30% by weight is preferred.

Other Additives

Although the composition according to the present invention essentiallycomprises of a thermoplastic synthetic resin, an inorganic flameretardant as described above and synthetic silicate, it may contain anantioxidant or lubricant for the purpose of enhancing the stability ofthe composition at processing, or a titanate or silane coupling agentfor the purpose of enhancing the adhesion of the filler to the matrix inan arbitrary amount in addition to the above essential componentswithout affecting the effect of the present invention.

Further, the composition of the present invention may also contain anorganic or inorganic pigment such as carbon black, azotype pigment,cyanine blue, cyanine green, iron oxide red or titanium oxide for thepurpose of coloring.

Function of the Invention

The synthetic silicate, i.e., non-crystalline silica to be used in thepresent invention has an amorphous steric chain of Si-O-Si-O in itsstructure. Therefore, it is estimated that when a synthetic silicatehaving such a structure is added to a halogen-free flame resistingsynthetic resin composition containing an inorganic flame retardant asdescribed above, a special flame resistant effect due to the flameresistant properties of the silicate itself and the steric flameresistant network formed in the composition be imparted to thecomposition. Thus substantially utilizing the generation of water by thedecomposition of the inorganic flame retardant and the endothermiceffect thereby.

Preparation of the composition of the present invention

The halogen-free flame resisting synthetic resin composition, accordingto the present invention may be prepared by using a master batchcomprising a thermoplastic synthetic resin, an inorganic retardant asdescribed above, synthetic silicate and other additives or by mixingthese components each in such an amount as to give its end-useconcentration and kneading the obtained mixture by an ordinary meanssuch as single-screw type extruder, twin-screw type extruder, roll millor Banbury mixer.

Further, synthetic silicate may be preliminarily added as such to theother components to obtain the composition of the present invention.Alternatively, a master batch comprising synthetic silicate and asynthetic resin may be added to a composition comprising a syntheticresin and an inorganic flame retardant as described above to therebyobtain the composition of the present invention.

Evaluation of the Invention

The evaluation of the composition according to the present invention iscarried out as follows: Namely, when a thermoplastic resin other thanpolystyrene or ABS was used, the resin, an inorganic flame retardant andother additives were mixed and the obtained mixture was kneaded in a 75l. Banbury mixer and processed with a mixing roll to obtain a sheethaving a thickness of 3 mm. This sheet was reprocessed with arectangular pelletizer to obtain a rectangular pellet having a length ofeach side of about 3 mm.

This rectangular pellet was repelletized with a 70φ extruder of a venttype at 150° C. to obtain a cylindrical pellet. This cylindrical pelletwas used as a sample.

The cylindrical pellet was examined for oxygen index according to JISK-7201. Further, the pellet was molded into a sheet having a thicknessof 200 μm with a T-die sheet molding machine to determine the combustionrate of the sheet with a flammability tester of FMVSS-302.

When polystyrene or ABS was used as the thermoplastic synthetic resin,the resulting composition was molded with an injection machine of 3.5ounce into a test bar according to the vertical flame test of UL-94 andthe test bar was further molded into a test piece having a thickness of1/8 inch. This test piece was used as a sample for the vertical flametest.

EXAMPLES AND COMPARATIVE EXAMPLES

The present invention will be described in more detail by referring tothe following Examples and Comparative Examples.

The components constituting the composition of each Example orComparative Example will be described, with the proviso that the amountsthereof used are shown in parts by weight and the comparative results ofthe compositions are shown in Tables 1 to 3.

EXAMPLE 1

    ______________________________________                                        low-density polyethylene (YUKARON HE-30                                                                  60.0   parts                                       mfd. by Mitsubishi Petrochemical Co., Ltd., MI: 0.3)                          magnesium hydroxide (KISUMA 5B mfd. by                                                                   40.0   parts                                       Kyowa Chemicals Co., Ltd., average particle                                   size: 0.8 μm)                                                              synthetic silicate (SILMOS-T mfd. by Shiraishi                                                           3.0    parts                                       Industrial Co., Ltd., SiO.sub.2 content: 60%)                                 total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 2

    ______________________________________                                        low-density polyethylene (the same as that used in                                                       55.0   parts                                       Example 1)                                                                    magnesium hydroxide (the same as that used                                                               45.0   parts                                       in Example 1)                                                                 synthetic silicate (the same as that used                                                                3.0    parts                                       in Example 1)                                                                 total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 3

    ______________________________________                                        low-density polyethylene (the same as that used in                                                       50.0   parts                                       Example 1)                                                                    magnesium hydroxide (the same as that used in                                                            50.0   parts                                       Example 1)                                                                    synthetic silicate (the same as that used in                                                             1.5    parts                                       Example 1                                                                     total                      101.5  parts                                       ______________________________________                                    

EXAMPLE 4

    ______________________________________                                        low-density polyethylene (the same as that used in                                                       50.0   parts                                       Example 1)                                                                    magnesium hydroxide (the same as that used in                                                            50.0   parts                                       Example 1)                                                                    synthetic silicate (the same as that used in                                                             3.0    parts                                       Example 1                                                                     total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 5

    ______________________________________                                        straight-chain low-density polyethylen                                                                   50.0   parts                                       (ULTZEX 3520F mfd. by Mitsui Petrochemical                                    Industries, Ltd. MI: 2.1)                                                     magnesium hydroxide (KX-4S mfd. by Asahi                                                                 50.0   parts                                       Glass Co., Ltd., average particle size: 0.6 μm)                            synthetic silicate (SILMOS-T mfd. by Shiraishi                                                           3.0    parts                                       Industrial Co., Ltd., SiO.sub.2 content: 60%                                  total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 6

    ______________________________________                                        high-density polyethylene (HIZEX 3300F                                                                   50.0   parts                                       mfd. by Mitsui Petrochemical Industries, Ltd.,                                MI: 0.9)                                                                      magnesium hydroxide (KISUMA 5B, the same                                                                 50.0   parts                                       as that used in Example 1)                                                    synthetic silicate (SOLEX CM mfd. by                                                                     3.0    parts                                       Tokuyama Soda Co., Ltd., SiO.sub.2 content: 57%)                              total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 7

    ______________________________________                                        ethylene-vinyl acetate copolymer (Evatate H                                                              50.0   parts                                       1011 mfd. by Sumitomo Chemical Co., Ltd., vinyl                               acetate content: 15%)                                                         magnesium hydroxide (KISUMA 5B, the same                                                                 50.0   parts                                       as that used in Example 1)                                                    synthetic silicate (SOLEX CM, the same                                                                   3.0    parts                                       as that used in Example 6)                                                    total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 8

    ______________________________________                                        polypropylene (JHG mfd. by Mitsui Toatsu                                                                 50.0   parts                                       Chemicals, Inc., MI: 4.0)                                                     magnesium hydroxide (KISUMA 5B, the same                                                                 50.0   parts                                       as that used in Example 1)                                                    synthetic silicate (SOLEX CM, the same                                                                   3.0    parts                                       as that used in Example 6)                                                    total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 9

    ______________________________________                                        low-density polyethylene (YUKARON HZ-30,                                                                 50.0   parts                                       the same as that used in Example 1)                                           aluminum hydroxide (HIGILITE H-42M mfd. by                                                               50.0   parts                                       Showa Light Metal Co., Ltd., average particle                                 size: 0.8 μm)                                                              synthetic calcium silicate (SOLEX CM, the                                                                3.0    parts                                       same as that used in Example 6)                                               total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 10

    ______________________________________                                        low-density polyethylene (YUKARON HZ-30, the                                  same as that used in Example 1)                                                                          50.0   parts                                       magnesium hydroxide (KISUMA 5B, the same as that used                         in Example 1)              50.0   parts                                       synthetic calcium silicate (SILMOS-T, the same as that                        used in Example 1)         7.0    parts                                       total                      107.0  parts                                       ______________________________________                                    

EXAMPLE 11

    ______________________________________                                        low-density polyethylen (YUKARON HZ-30, the                                   same as that used in Example 1)                                                                          50.0   parts                                       aluminium hydroxide (HIGILITE H-42M mfd. by                                   Showa Light Metal Co., Ltd., average particle                                 size of 0.8 μm)         50.0   parts                                       synthetic calcium silicate (SILMOS-T,                                         the same as that used in Example 1)                                                                      10.0   parts                                       total                      110.0  parts                                       ______________________________________                                    

EXAMPLE 12

    ______________________________________                                        polystyrene (STYRON 470 mfd. by Asahi Chemical                                Industry Co., Ltd., MI:4.0)                                                                              50.0   parts                                       magnesium hydroxide (KISUMA 5B, the same as                                   that used in Example 1)    50.0   parts                                       synthetic calcium silicate (SILMOS-T,                                         the same as that used in Example 1)                                                                      3.0    parts                                       total                      103.0  parts                                       ______________________________________                                    

EXAMPLE 13

    ______________________________________                                        ABS (DENKA OF mfd. by Denki Kagaku                                            Kogyo K.K.)                50.0   parts                                       magnesium hydroxide (KISUMA 5B, the same as                                   that used in Example 1)    50.0   parts                                       synthetic calcium silicate (SILMOS-T,                                         the same as that used in Example 1)                                                                      3.0    parts                                       total                      103.0  parts                                       ______________________________________                                    

COMPARATIVE EXAMPLE 1

    ______________________________________                                        low-density polyethylene (YUKARON HZ-30                                       mfd. by Mitsubishi Petrochemical Co., Ltd., MI:0.3)                                                      60.0   parts                                       magnesium hydroxide (KISUMA 5B, mfd. by Kyowa                                 Chemicals Co., Ltd., average particle size: 0.8 μm)                                                   40.0   parts                                       total                      100.0  parts                                       ______________________________________                                    

COMPARATIVE EXAMPLE 2

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)     55.0   parts                                       magnesium hydroxide (the same as that used in                                 Comparative Example 1)     45.0   parts                                       total                      100.0  parts                                       ______________________________________                                    

COMPARATIVE EXAMPLE 3

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)     50.0   parts                                       magnesium hydroxide (the same as that used in                                 Comparative Example 1)     50.0   parts                                       total                      100.0  parts                                   

COMPARATIVE EXAMPLE 4

    ______________________________________                                        straight-chain low-density polyethylene                                       (ULTZEX 2020L mfd. by Mitsui Petrochemical                                    Industries, Ltd., MI:2.1)                                                                              50.0    parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)   50.0    parts                                        total                    100.0   parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 5

    ______________________________________                                        high-density polyethylene (HIZEX 3300F mfd. by                                Mitsui Petrochemical Industries, Ltd., MI:0.9)                                                          50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        total                     100.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 6

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)    50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        crystalline silica (TOKUSIL U mfd. by Tokuyama                                Soda Co., Ltd., SiO.sub.2 content: 95%)                                                                 3.0    parts                                        total                     103.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 7

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)    50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        mica (Mica #300 mfd. by Repco, average particle                               size: 2 μm)            3.0    parts                                        total                     103.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 8

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)    50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        calcium magnesium carbonate (Pigment white 18A                                mfd. by Shiraishi Industrial Co., Ltd., average                               particle size: l μm)   3.0    parts                                        total                     103.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 9

    ______________________________________                                        low-density polyethylene (the same as that used in                            Comparative Example 1)    50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        carbon black (Mitsubishi MB #30 mfd. by                                       Mitsubishi Chemical Industries, Ltd.)                                                                   3.0    parts                                        total                     103.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 10

    ______________________________________                                        polystyrene (STYRON 470 mfd. by Asahi                                         chemical Industry Co., Ltd., MI: 4.0)                                                                   50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        total                     100.0  parts                                        ______________________________________                                    

COMPARATIVE EXAMPLE 11

    ______________________________________                                        ABS (DENKA OF mfd. by Denki Kagaku Kogyo                                      K.K.)                     50.0   parts                                        magnesium hydroxide (the same as that used in                                 Comparative Example 1)    50.0   parts                                        total                     100.0  parts                                        ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                        Results of Examples using crystalline olefin                                                 Flame             Oxy-  combustion                                   Synthetic                                                                              resistant         gen   rate                                   No.   resin    filler   Additive index (mm/min)                               ______________________________________                                        Ex. 1 60.0     40.0     3.0      24.0  68.0                                         LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 2 55.0     45.0     3.0      27.0  46.0                                         LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 3 50.0     50.0     1.5      29.2  o                                            LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 4 50.0     50.0     3.0      30.4  o                                            LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 5 50.0     50.0     3.0      30.2  o                                            LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 6 50.0     50.0     3.0      29.6  o                                            HDPE     Mg(OH).sub.2                                                                           SOLEX CM                                              Ex. 7 50.0     50.0     3.0      30.4  o                                            EVA      Mg(OH).sub.2                                                                           SOLEX CM                                              Ex. 8 50 0     50.0     3.0      29.8  o                                            PP       Mg(OH).sub.2                                                                           SOLEX CM                                              Ex. 9 50.0     50.0     3.0      29.4  o                                            LDPE     Al(OH).sub.3                                                                           SOLEX CM                                              Ex. 10                                                                              50.0     50.0     7.0      30.0  o                                            LDPE     Mg(OH).sub.2                                                                           SILMOS-T                                              Ex. 11                                                                              50.0     50.0     10.0     29.8  o                                            LDPE     Al(OH).sub.3                                                                           SILMOS-T                                              ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Results of Comparative Examples using                                         crystalline olefin                                                                           Flame                   Combustion                                   Synthetic                                                                              resistant        Oxygen rate                                   No.   resin    filler   Additive                                                                              index  (mm/min)                               ______________________________________                                        Comp. 60.0     40.0     --      22.4   180.0                                  Ex. 1 LDPE     Mg(OH).sub.2                                                   Comp. 55.0     45.0     --      24.2   78.0                                   Ex. 2 LDPE     Mg(OH).sub.2                                                   Comp. 50.0     50.0     --      25.2   76.0                                   Ex. 3 LDPE     Mg(OH).sub.2                                                   Comp. 50.0     50.0     --      24.8   84.0                                   Ex. 4 LDPE     Mg(OH).sub.2                                                   Comp. 50.0     50.0     --      25.4   80.0                                   Ex. 5 HDPE     Mg(OH).sub.2                                                   Comp. 50.0     50.0     3.0     25.6   67.0                                   Ex. 6 LDPE     Mg(OH).sub.2                                                                           crystalline                                                                   silica                                                Comp. 50.0     50.0     3.0     25.2   73.0                                   Ex. 7 LDPE     Mg(OH).sub.2                                                                           mica                                                  Comp. 50.0     50.0     3.0     25.0   81.0                                   Ex. 8 LDPE     Mg(OH).sub.2                                                                           carbonate                                             Comp. 50.0     50.0     3.0     29.4   o                                      Ex. 9 LDPE     Mg(OH).sub.2                                                                           carbon                                                                        black                                                 ______________________________________                                         (note)                                                                        LDPE refers to lowdensity polyethylene, HDPE refers to highdensity            polyethylene and EVA refers to ethylenevinyl acetate copolymer. The symbo     "o" in the column of combustion rate means that the test sheet or test        piece did not burn up to the mark, i.e., that the test sheet or test piec     was selffire extinguishable.                                             

                  TABLE 3                                                         ______________________________________                                        Examples and Comparative Examples using                                       styrenic resin                                                                               Flame                                                                Synthetic                                                                              resistant         Oxygen  UL 94                                No.   resin    filler    Additive                                                                              index   (1/8")                               ______________________________________                                        Ex. 12                                                                              50.0     50.0      3.0     29.0    V-1                                        PS       Mg(OH).sub.2                                                                            SILMOS-T                                             Ex. 13                                                                              50.0     50.0      3.0     29.4    V-1                                        ABS      Mg(OH).sub.2                                                                            SILMOS-T                                             Comp. 50.0     50.0      --      26.0    HB                                   Ex. 10                                                                              PS       Mg(OH).sub.2                                                   Comp. 50.0     50.0      --      25.6    HB                                   Ex. 11                                                                              ABS      Mg(OH).sub.2                                                   ______________________________________                                         (note)                                                                        PS refers to polystyrene.                                                     "V-1" means that the flame of the test piece guttered out within 30           seconds after contacting the test piece with flame.                           "HB" means that the test is did not burn until the mark in the horizontal     flame test, though the test piece did not fit the vertical flame test.   

INDUSTRIAL APPLICABILITY

According to the present invention, a white semi-translucent syntheticresin composition which is highly flame resistant and does not generateany toxic substance can be obtained, though such a composition can notbe obtained according to the prior art. The flame resisting syntheticresin composition of the present invention will be able to be used in awide field requiring color discrimination, for example, floor materialsof a nuclear power station.

What is claimed is:
 1. A self-extinguishing, halogen-free flameretardant composition comprising 70 to 30 parts by weight of at leastone thermoplastic synthetic resin, 30-70 parts by weight of magnesiumhydroxide having an average particle size of 0.1 to 10 μm, and 0.5-15parts by weight of a synthetic silicate which is a non-crystallinesilica having an amorphous steric chain of Si-O-Si-O in its structure.2. The composition as defined by claim 1 wherein said at least onethermoplastic resin is selected from the group consisting of low-densitypolyethylene, high density polyethylene, ethylene-vinyl acetatecopolymer, ethylene-ethyl acrylate copolymer, ethylene-methylmethacrylate copolymer, polypropylene, polystyrene, polyacrylonitrile,acrylonitrile-butadiene-styrene copolymer, nylon 6, and nylon-6,6. 3.The composition as defined by claim 1 wherein said thermoplasticsynthetic resin has a melt index of 0.2 to 10.0.
 4. The composition asdefined by claim 1 wherein said synthetic silicate comprises 40 to 70%by weight SiO₂ and 10 to 45% by weight MgO and CaO.
 5. The compositionas defined by claim 4 wherein said synthetic silicate comprises 50 to60% by weight SiO₂, 12 to 30% by weight MgO and CaO, and an ignitionloss of 10 to 30% by weight.
 6. The composition as defined by claim 1wherein the sum of said thermoplastic synthetic resin and said magnesiumhydroxide equals 100 parts by weight.
 7. A self-extinguishing,halogen-free, flame retardant composition comprising 70 to 30 parts byweight of at least one thermoplastic synthetic resin, 30-70 parts byweight of magnesium hydroxide having an average particle size of 0.6 to0.08 μm, and 0.5-15 parts by weight of a synthetic silicate salt.
 8. Thecomposition as defined by claim 7 wherein said at least onethermoplastic resin is selected from the group consisting of low-densitypolyethylene, high density polyethylene, ethylene-vinyl acetatecopolymer, ethylene-ethyl acrylate copolymer, ethylene-methylmethacrylate copolymer, polypropylene, polystyrene, polyacrylonitrile,acrylonitrile-butadiene-styrene copolymer, nylon 6, and nylon-6,6. 9.The composition as defined by claim 7 wherein said thermoplasticsynthetic resin has a melt index of 0.2 to 10.0.
 10. The composition asdefined by claim 7 wherein said synthetic silicate comprises 40 to 70%by weight SiO₂ and 10 to 45% by weight MgO and CaO.
 11. The compositionas defined by claim 10 wherein said synthetic silicate comprises 50 to60% by weight SiO₂, 12 to 30% by weight MgO and CaO, and an ignitionloss of 10 to 30% by weight.
 12. The composition as defined by claim 7wherein the sum of said thermoplastic synthetic resin and said magnesiumhydroxide equals 100 parts by weight.